1) Field of the Invention
The present invention relates to friction stir welding and, more particularly, to positioning a structural assembly for friction stir welding and friction stir welding the structural assembly to form a preform.
2) Description of Related Art
Friction stir welding is a process in which a rotating tool, such as a pin or probe, is urged into and/or through a workpiece, e.g., to join multiple members of the workpiece in a solid state or to repair cracks in a workpiece. Typically, the pin extends from a shoulder, which can be flat, concave, or otherwise contoured, and the shoulder is urged against the workpiece so that the pin is urged therein. The pin is then urged through the workpiece to form a continuous weld joint. For example, during one conventional friction stir welding process, the probe of the rotating tool is plunged into a workpiece or between two workpieces by a friction stir welding machine to produce the required resistance force to generate sufficient frictional heating to form a region of plasticized material. The tool can be tilted approximately 3° relative to the workpiece such that the trailing edge of the shoulder is thrust into and consolidates the plasticized material. Upon solidification of the plasticized material, the members of the workpiece are joined along the weld joint. The magnitude of force exerted by the friction stir welding tool must be maintained above a prescribed minimum in order to generate the required frictional heating. Friction stir welding is further described in U.S. Pat. No. 5,460,317 to Thomas et al., the contents of which are incorporated herein by reference.
Friction stir welding has been demonstrated to be a successful joining method for forming certain types of joints, such as the butt joint where the probe is inserted between abutting edges of two structural members, or a lap joint in which the probe is inserted in a direction substantially perpendicular to the interface between overlapping structural members. In addition, other types of friction welding have also been shown to be useful for forming certain joints.
Methods have also been used to friction stir weld preforms. One method includes inserting the probe through a structural member to one side of a center web substrate. Structural members are then added to the opposed second side of the substrate by turning the part over and inserting the probe through the additional structural members and into the substrate to weld the entire structure together. A second method involves welding the structural member to the substrate by inserting the probe through the substrate and into the underlying structural member. A second structural member is stacked on top of the substrate (opposite the previously welded structural member), and the probe is inserted through the second structural member and into the substrate to weld the structure together. Both methods require that each structural member be separately clamped for welding, which is expensive and time consuming. In addition, the second method does not address friction stir welding fully within the structural member.
It would therefore be advantageous to provide a system for friction stir welding preforms that is relatively inexpensive and effective. It would also be advantageous to provide an assembly to secure structures having various sizes during friction stir welding of preforms. It would further be advantageous to provide an assembly that promotes efficient assembly and disassembly before and after friction stir welding the structures into a preform.